No. 566] EDAPHOSAURUS CRUCIGER 



125 



The point which concerns the present discussion is that not 

 only does humidity have a definite regularly acting influence, but 

 that its results are similar to those of temperature and, as with 

 temperature, plus and minus variations of certain intensities 

 bring about similar effects. If, as has usually happened, the hu- 

 midity is not controlled in experimental work on the effect of 

 temperature, how can it be said that the observed results are the 

 effect of changes in temperature ? 



Tower made certain experiments in which both temperature 

 and humidity are abnormal, normal average temperature being 

 taken as 22.2° C. Unfortunately, proof reading or something of 

 the sort was faulty when it came to publication. Experiment 

 26 would be the most valuable for our present purpose, but the 

 table includes records of relative humidity 35 and 39 per cent, 

 above normal, i. e., relative humidities of 109 and 113 per cent., 

 respectively, if, as in the other experiments, 74 per cent, is 

 ''normal" humidity. These are clearly impossible. The text 

 figure illustrating this experiment does not help us since hu- 

 midities are not given and furthermore the temperatures in the 

 figure are rather consistently one degree different from those 

 given in the table. Since there are two errors in text-figure 15, 

 which illustrates the experiments with humidity as the only vari- 

 able, it is likely that the figure is the thing that is at fault here. 

 Several other similar discrepancies could be pointed out (as, for 

 example, the temperatures in experiment 24. which concerns the 

 combination effect of humidity and temperature) but it is prob- 

 able that the author's notebook records are correct and the tem- 

 perature discrepancies in the published report are so slight that 

 we may accept his conclusion. It is 



that when temperature and moisture are the variables in a given en- 

 vironmental complex, the trend of general color modification is con- 

 trolled by moisture (relative humidity), excepting in conditions where 

 the temperature deviation is so excessive that the ordinary physiological 

 and developmental processes are greatly inhibited. In experiments 



the dominant factor in influencing coloration. 



Even if there were no other reasons for urging the necessity 

 of taking humidity into account, I feel that Tower's work would 

 be ample justification. Before taking up those reasons let us 

 notice several cases where, on account of the striking results of 

 the experiments, we must regret our lack of information as to the 

 real cause or the relation of the several causes. 



